Dry etching method and semiconductor device manufacturing method

ABSTRACT

In a method for dry-etching a coating by use of reactive gas which is activated, a second insulating layer containing carbon atoms which is formed on a first insulating layer containing carbon atoms is ashed by use of a gas containing carbon atoms and at least one of oxygen atoms, nitrogen atoms and hydrogen atoms. By using the above gas, the second insulating layer containing carbon atoms which is formed on the first insulating layer which is an underlying layer can be efficiently ashed and removed without removing carbon atoms in the side surface of the grooves formed in the first insulating layer and etching the side surface thereof. Thus, the side surface of the groove formed in the first insulating layer will not be modified or deformed.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 11-372006, filed Dec. 28,1999, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a dry etching method for eliminating asecond insulating layer containing carbon atoms formed on a firstinsulating layer containing carbon atoms by use of activated reactivegas and a semiconductor device manufacturing method using the dryetching method.

[0003] A semiconductor device is required to have a more fine patternwith an increase in the integration density thereof. Further, an attemptis made to reduce an interconnection resistance and parasitic resistancein order to enhance the response speed.

[0004] In order to enhance the fine pattern technique of thesemiconductor device, it is necessary to improve the resolution of aphotoresist and it is effective to reduce the thickness of thephotoresist in the development of the semiconductor device. Further, anantireflection layer is formed directly under a photoresist layer andthe photoresist layer is patterned.

[0005] It is required to lower the interconnection parasitic capacitancein order to enhance the operation speed of the semiconductor device anda lowering in the dielectric constant (which is called Low-k layer) ofan interlayer dielectric is studied. As the interlayer dielectric havinga lowered dielectric constant, an organic based layer such as CF(fluorocarbon) based Teflon, a porous and relatively fragile inorganiclayer such as an inorganic silicon oxide layer and an organic siliconoxide layer containing an organic component having carbon atoms in aninorganic layer can be given. The relative dielectric constant of theconventional oxide layer is approximately 4, but the relative dielectricconstant of the above insulating layers is 3 or less. If an etchingprocess is effected to form interconnection grooves and contact holesafter a photoresist is patterned on the interlayer insulating layer, itis necessary to strip the photoresist in order to prepare for a casewherein an interconnection material or the like is filled in a laterstep.

[0006] In the conventional photoresist stripping method, a downflowashing process for raising the wafer temperature to a high temperatureof 200° C. or more and using process gas mainly containing oxygen gas iseffected. In this method, the resist stripping process is realized byreacting carbon, oxygen, hydrogen atoms and the like in the photoresistwith oxygen atoms in the active gas. It is considered that a reactiveproduct obtained at this time contains CO₂, CO, H₂O and the like, but inorder to attain a sufficiently high stripping rate, a method for raisingthe temperature of the semiconductor substrate to 200° C. or more toenhance the reactivity is normally used.

[0007] However, in the conventional photoresist stripping method, if amulti-layered layer having a layer containing carbon atoms is formed asan underlying layer, the carbon atoms of the underlying layer react withoxygen atoms in the active gas and are removed. Therefore, if theunderlying layer of the photoresist layer is a Teflon based organiclayer (Low-k layer) of CF series, the underlying layer is etched whenthe photoresist is stripped and there occurs a problem that a criticaldimension bias (CD bias) occurs. Further, if the underlying layer is alayer (organic silicon oxide layer) formed of an inorganic layercontaining carbon atoms, a carbon atom removed layer is formed on thesurface of the underlying layer and a problem that the relativedielectric constant is changed occurs. At this time, since theunderlying layer from which the carbon atoms have been removed iscontracted, there occurs a problem that not only the CD bias is changedbut also a stress is applied, thereby causing a crack.

[0008] Further, as a gas dielectric structure, a structure having acarbon layer buried in a porous insulating layer used as the underlyinglayer is known. The structure is formed by sequentially effectingprocesses for stripping the photoresist after interconnection groovesand contact holes are formed in the carbon layer, then filling barriermetal and interconnection material therein, and effecting a CMP(Chemical Mechanical Polishing) step. However, in the conventionalmethod, there occurs a problem that carbon atoms buried in theunderlying layer are ashed at the time of stripping the photoresist, theunderlying layer is partly removed and, as a result, the CD bias occurs.

BRIEF SUMMARY OF THE INVENTION

[0009] This invention has been made in view of the above problems and anobject of this invention is to provide a dry etching method andsemiconductor device manufacturing method for preventing modification ordeformation from occurring on the side surface of grooves when a secondinsulating layer is removed after the second insulating layer which ispatterned and contains carbon is formed on a first insulating layercontaining carbon and the grooves are formed in the first insulatinglayer with the second insulating layer used as a mask.

[0010] In order to attain the above object, a dry etching method of afirst aspect of this invention comprises the steps of sequentiallylaminating a first insulating layer containing carbon and a secondinsulating layer containing carbon on a substrate; patterning the secondinsulating layer into a preset shape; forming grooves in the firstinsulating layer by etching the first insulating layer with the secondinsulating layer used as a mask; and removing the second insulatinglayer by use of a reactive gas containing carbon atoms and at least oneof oxygen atoms, hydrogen atoms and nitrogen atoms without substantiallymodifying or deforming the side surface of the grooves formed in thefirst insulating layer.

[0011] It is preferable that the first insulating layer containingcarbon atoms is one selected from a group consisting of a carbon layer,an organic silicon compound layer and an organic layer.

[0012] The second insulating layer containing carbon is a photoresist,for example.

[0013] A semiconductor device manufacturing method of a second aspect ofthis invention comprises the steps of sequentially laminating aninsulating layer and photoresist each containing carbon on asemiconductor substrate; patterning the photoresist into a preset shape;forming at least one of contact holes and a interconnection grooves inthe insulating layer by etching the insulating layer with thephotoresist used as a mask; ashing and removing the photoresist by useof a gas containing carbon atoms and at least one of oxygen atoms,hydrogen atoms and nitrogen atoms; and depositing a metalinterconnection layer in at least one of the contact holes and theinterconnection grooves to form interconnections therein.

[0014] It is preferable that the insulating layer containing carbon isone of an organic silicon compound layer and an insulating layer of lowdielectric constant containing carbon atoms.

[0015] A semiconductor device manufacturing method of a third aspect ofthis invention comprises the steps of sequentially laminating aninsulating layer and a first photoresist on a semiconductor substrate;patterning the first photoresist into a preset shape; forming firstinterconnection grooves by etching the insulating layer with the firstphotoresist used as a mask; ashing and removing the first photoresist byuse of a gas containing carbon atoms and at least one of oxygen atoms,hydrogen atoms and nitrogen atoms; burying a carbon layer in the firstinterconnection grooves; laminating a second photoresist on theinsulating layer to cover the carbon layer; patterning the secondphotoresist into a preset shape; forming second interconnection groovesby etching the carbon layer with the second photoresist used as a mask;ashing and removing the second photoresist by use of a gas containingcarbon atoms and at least one of oxygen atoms, hydrogen atoms andnitrogen atoms; depositing a metal interconnection layer in the secondinterconnection grooves to bury interconnections therein; forming aporous silicon oxide layer on the interlayer insulating layer to coverthe interconnections and the carbon layer; and heating the carbon layerto remove the same from the interconnection grooves and provide a hollowaround each of the interconnections.

[0016] It is preferable that the step of sequentially laminating aninsulating layer and a first photoresist on a semiconductor substrateand the step of laminating a second photoresist on the insulating layerto cover the carbon layer further include a step of forming anantireflection layer between the insulating layer and the first orsecond photoresist.

[0017] In the first to third aspects, it is preferable to realize thefollowing items.

[0018] (1) Among the gas containing carbon atoms and at least one ofoxygen atoms, hydrogen atoms and nitrogen atoms, the atomic percentageof carbon in a gas containing oxygen atoms and carbon atoms is ⅓or moreof the atomic percentage of oxygen.

[0019] (2) As gas containing oxygen atoms and carbon atoms among the gascontaining carbon atoms and at least one of oxygen atoms, hydrogen atomsand nitrogen atoms, a gas selected from a gas containing oxygen andcarbon dioxide, a gas containing oxygen and carbon monoxide, a carbonmonoxide gas and a carbon dioxide gas is used.

[0020] (3) The step of ashing and removing the photoresist includes astep of setting the substrate temperature to 150° C. or less.

[0021] (4) The step of ashing and removing the photoresist includes astep of setting the reaction pressure to 400 m Torr or less.

[0022] Conventionally, the operation for stripping the photoresist afterforming the insulating layer (for example, Low-k layer) containingcarbon atoms is effected by a plasma ashing process by use of an oxygengas, but according to this method, the side surfaces of the Low-k layerare also side-etched at the same time as the upper portion thereof isetched, and thus there occurs a problem that a CD bias occurs. This isbecause an isotropic oxygen radical component enters the contact holeformed in the Low-k layer at the time of plasma ashing of thephotoresist by use of an oxygen gas and etching of the Low-k layerproceeds starting from a portion which is in contact with the radicalbased gas.

[0023] This invention is characterized in that a second insulating layer(for example, photoresist) containing carbon atoms which is formed on afirst insulating layer (for example, Low-k layer) containing carbonatoms is ashed by use of a gas containing carbon atoms and at least oneof oxygen atoms, hydrogen atoms and nitrogen atoms in a method fordry-etching a coating by use of a reactive gas which is activated asdescribed above. By using the above gas, a phenomenon that the firstunderlying insulating layer is oxidized and the carbon atoms are removedcan be suppressed and only the second insulating layer containing carbonatoms can be efficiently removed by ashing. Thus, formation of amodified layer on the side surface of the groove in the first insulatinglayer and the side etching thereof can be prevented.

[0024] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0025] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0026]FIGS. 1A to 1E are cross sectional views of a semiconductor deviceshowing the manufacturing method in the order of steps of manufacturingthe semiconductor device according to a first embodiment of thisinvention;

[0027]FIG. 2 is a schematic view of an ashing device used in theembodiment of this invention;

[0028]FIG. 3 is a characteristic diagram showing the relation betweenthe photoresist ashing rate and the thickness of a modified layer orcarbon removed layer on the side wall of the contact hole of theunderlying layer at the time of ashing with respect to the gascomposition ratio of an ashing gas having carbon monoxide contained inan oxygen gas;

[0029]FIG. 4 is a characteristic diagram showing the relation betweenthe photoresist ashing rate and the thickness of a modified layer orcarbon removed layer on the side wall of the contact hole of theunderlying layer with respect to the carbon atom density of an ashinggas;

[0030]FIG. 5 is a characteristic diagram showing the relation betweenthe photoresist ashing rate and the thickness of a modified layer orcarbon removed layer on the side wall of the contact hole of theunderlying layer at the time of ashing with respect to the gascomposition ratio of an ashing gas containing carbon dixoide;

[0031]FIG. 6 is a characteristic diagram showing the relation betweenthe photoresist ashing rate and the thickness of a modified layer on theside wall of the contact hole of the underlying layer at the time ofashing with respect to the substrate temperature in a case whereinoxygen and carbon monoxide are used as an ashing gas;

[0032]FIG. 7 is a characteristic diagram showing the relation betweenthe photoresist ashing rate and the thickness of a modified layer on theside wall of the contact hole of the underlying layer at the time ofashing with respect to the gas pressure in a case wherein oxygen andcarbon monoxide are used as an ashing gas;

[0033]FIGS. 8A to 8E are cross sectional views of a semiconductor deviceshowing the manufacturing method in the order of steps of manufacturingthe semiconductor device according to a second embodiment of thisinvention; and

[0034]FIGS. 9A to 9K are cross sectional views of a semiconductor deviceshowing the manufacturing method in the order of steps of manufacturingthe semiconductor device according to a third embodiment of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] There will now be described embodiments of this invention withreference to the accompanying drawings.

[0036] (First Embodiment)

[0037] A semiconductor device manufacturing method according to a firstembodiment of this invention is explained with reference to FIGS. 1A to1E. First, a low dielectric constant insulating layer (which ishereinafter referred to as an LKD layer) 12 with a film thickness 500 nmis formed by coating as an interlayer dielectric on a semiconductorsubstrate 11 formed of silicon semiconductor. A metal interconnection 10such as an aluminum layer is buried in the surface portion of the LKDlayer 12. An LKD layer 13 with a film thickness 400 nm is formed bycoating as an interlayer dielectric on the LKD layer 12. The LKD layer13 is formed of an organic silicon oxide layer such as a polysiloxanelayer or benzocyclobutene (BCB) layer with the structure containingcarbon atoms in an inorganic based layer.

[0038] In addition, the LKD layer may be formed of an inorganic siliconoxide layer which is formed of hydrogen-silsesquioxane or a CF basedlayer which is formed of poly (arylene) ether, parylene-AF4, polyimide,fluoropolymer, for example.

[0039] A modified layer 14 which is an oxide layer is formed bysubjecting the semiconductor substrate (wafer) to an oxygen plasmaprocess. An antireflection layer 15 formed of an organic material with afilm thickness 60 nm and a photoresist 16 with a film thickness 0.6 μmare formed on the above layer. After this, the photoresist 16 ispatterned by a lithography technique which is well known in the art(FIG. 1A).

[0040] Next, the antireflection layer is etched with the patternedphotoresist 16 used as a mask (FIG. 1B). Then, the modified layer 14 andLKD layer 13 are an etched by an RIE (reactive ion etching) method usingan etching gas of C₄F₈/CO/O₂/Ar to form a contact hole with a depth of400 nm and a pattern size of 0.2 μm. On the bottom surface of thecontact hole, the metal interconnection 10 buried in the LKD layer 12 isexposed (FIG. 1C).

[0041] Next, portions of the photoresist 16 and antireflection layer 15which are left behind on the LKD layer 13 are stripped (FIG. 1D). Afterthis, a TiN barrier metal layer 18 is formed to a film thickness ofapproximately 30 nm on the modified layer 14 and the inner wall of thecontact hole. Then, an aluminum (Al) layer 19 is formed to a filmthickness of 700 nm by sputtering and filled in the contact hole. Afterthis, the Al layer 19 is polished by a CMP method until the surfacelayer of the LKD layer 13 is exposed. Thus, the aluminum layer 19 usedas a contact interconnection is formed in the contact hole. The aluminumlayer 19 is used for electrically connecting an upper layerinterconnection (not shown) of aluminum formed on the interlayerdielectric 13 later step to the metal interconnection (lower layerinterconnection) 10 (FIG. 1E).

[0042] The metal interconnection used in this invention is not limitedto aluminum. For example, Al—Si—Cu, Al—Cu, W, WSi, Cu, Ag, Au or thelike can be used. Further, the above materials can be used for a contactinterconnection for connecting the metal interconnections to each other.The interconnections can be formed of the same material or differentmaterials. The materials can be freely selected by taking thecharacteristic of the semiconductor element and the like intoconsideration. In the first embodiment, the LKD layer is formed bycoating but it can be formed by use of a CVD (Chemical Vapor Deposition)method. Further, the contact hole is formed in this embodiment, but thisinvention can be applied when interconnections or other patterns areformed, for example.

[0043]FIG. 2 is a cross sectional view schematically showing an ashingdevice. A mounting table 3 for mounting a to-be-processed object 2 suchas a silicon wafer thereon is provided in a vacuum chamber 1. Anopposite electrode 6′ is provided in opposition to the mounting table 3.The mounting table 3 has a temperature adjusting mechanism so as tocontrol the temperature of the to-be-processed object 2. On the ceilingwall of the vacuum chamber, a gas inlet pipe 4 is connected. Gas isintroduced into the vacuum chamber via the gas inlet pipe 4 and thepressure is adjusted by use of a valve (not shown) of an exhaust port 5.After the pressure becomes stable, plasma is generated in the vacuumchamber by applying RF (Radio Frequency) power from an RF power source 6disposed below the mounting table 3 so as to ash the to-be-processedobject 2.

[0044] In the first embodiment, the ashing device of FIG. 2 is used, butthis invention can use an ashing device having another plasma source.Further, an asher device (for example, downflow asher device (includingan asher device using microwaves)) other than the plasma ashing devicecan be used.

[0045] In the first embodiment, for example, formation of the layer suchas a photoresist containing carbon atoms is performed by a plasmaprocess using a gas containing a new material containing oxygen atomsand carbon atoms. The ashing device is a parallel plate ashing deviceshown in FIG. 2 and the ashing condition is O₂/CO= 100/200 ccm, 100 mTorr, 500 W, 30° C.

[0046] In FIG. 3, the ordinate on the left side corresponds to a curveindicated by a solid line and indicates the ashing rate (nm/min) of thephotoresist. The ordinate on the right side indicates the thickness(corresponding to a curve indicated by a dotted line) of a side wallmodified layer of the LKD layer which is used as an underlying layerwhen the photoresist is ashed by 300 nm, the ordinate on the right sidealso indicates the thicknesses (nm) in cases wherein a CF based layerand C based layer are removed (respectively corresponding to curvesindicated by a chain line and a chain double-dashed line). The abscissaindicates the CO concentration (mol %) (CO/(O₂+CO)) of ashing gas.

[0047] As shown in FIG. 3, if the condition other than the COconcentration of the ashing gas is set to the condition described above,the CF based layer is ashed and the CO concentration is set to 67% ormore, then the etching rate is slightly lowered, but occurrence of theside etching can be prevented. The same effect can be attained in a caseof the LKD layer and CF based layer.

[0048]FIG. 4 shows a case wherein CO in the ashing gas of FIG. 3 isreplaced by CO₂ and a case wherein O₂ gas is independently used incomparison with a case wherein (O₂+CO) gas is used. The ordinate isdefined in the same manner as in FIG. 3 and the abscissa indicates acarbon content (atomic %) of ashing gas formed of O₂ gas and X gas (inthis case, X/(O₂+X)=⅔). In FIG. 4, the A point indicates a case whereinO₂ gas is independently used (conventional case), the B point indicatesa case wherein X=CO₂ and the C point indicates a case wherein X=CO.Thus, in a process gas containing oxygen atoms and carbon atoms, thesuppressing effect of the side etching is particularly high in a regionin which the percentage of carbon atoms is ⅓or more of the percentage ofoxygen atoms (in the right region with respect to the C point in FIG.4). In the C point, C=30 is obtained based on CO/(O₂+CO)=⅔.

[0049] Further, in this invention, when oxygen gas is used as acomponent of ashing gas, the component does not mean that oxygen gas isexclusively used, but it is possible that the component may contain oneor both of a nitrogen gas and a hydrogen gas.

[0050]FIG. 5 is a characteristic diagram when a gas formed of O₂ and CO₂is used as ashing gas. The ordinate is defined in the same manner as inFIG. 3 and the abscissa indicates the CO₂ concentration (mol %)(CO₂/(O₂+CO₂)) of the ashing gas. The effect is slightly lowered incomparison with the case of a CO gas due to a greater O content in a CO₂gas, shown in FIG. 3, but if the CO₂ concentration of the ashing gas isset to 75% or more, the C based layer can be ashed without causingsubstantial side etching.

[0051] As shown in FIGS. 3 and 5, it is clearly understood that the sameeffect can be attained even when only CO gas or CO₂ gas is used withoutusing oxygen gas (that is, even when CO or CO₂ is 100%). Therefore, inthis invention, a gas consisting of O₂ and CO₂, a gas consisting of O₂and CO, a CO gas or a CO₂ gas can be used as a gas containing oxygenatoms and carbon atoms.

[0052] After the process for forming holes in the LKD layer 13, thephotoresist is stripped by the plasma ashing process independently usingan oxygen gas in the conventional method, but in this case, there occursa problem that carbon atoms are removed from the side wall of the LKDlayer 13 and a modified layer (side wall carbon removed layer) isformed. The reason for this is considered as follows.

[0053] In the low pressure oxygen ashing, ion assisted etching of thephotoresist due to an oxygen ion and oxygen radical occurs. At thistime, an isotropic oxygen radical component enters the contact hole andcarbon atoms are removed from a portion which is in contact with theradical. Further, spreading of the CD bias occurs by removal of carbonatoms from the layer.

[0054] Therefore, in the first embodiment, stripping of the photoresist16 and antireflection layer 15 is effected by a plasma process using agas containing oxygen atoms and carbon atoms. The ashing device is of aparallel plate type shown in FIG. 2 and the ashing condition is so setthat the flow rate of O₂ is 30 ccm, the flow rate of CO is 270 ccm, thepressure is 100 m Torr, the power is 500 W and the temperature is 30° C.As shown in FIG. 3, in this condition, the process for stripping thephotoresist proceeds, and since removal of carbon atoms from the sidewall of the LKD layer can be prevented, formation of the side wallmodified layer can be sufficiently suppressed.

[0055] Further, as shown in FIG. 6, by effecting the plasma ashingprocess at 150° C. or less, removal of carbon atoms from the side wallof the LKD layer which is an underlying layer can be suppressed whilethe resist ashing rate is kept sufficiently high. In FIG. 6, the leftside ordinate indicates the ashing rate (nm/min) of the photoresist, theright side ordinate indicates the thickness (nm) of the side wallmodified layer of the LKD layer which is an underlying layer when thephotoresist is ashed by 300 nm, and the abscissa indicates the etchingtemperature (° C.) of the semiconductor substrate. Further, the pressureat the time of ashing is 100 m Torr.

[0056] As shown in FIG. 7, by effecting the process while setting thepressure at 400 m Torr or less, removal of carbon from the side wall ofthe LKD layer which is an underlying layer can be more effectivelysuppressed. In FIG. 7, the left side ordinate indicates the ashing rate(nm/min) of the photoresist, the right side ordinate indicates thethickness (nm) of the side wall modified layer of the LKD layer which isan underlying layer when the photoresist is ashed by 300 nm, and theabscissa indicates the pressure (Torr) at the time of ashing. Further,the temperature at the time of ashing is 30° C.

[0057] As described in the first embodiment, the layer (photoresist)containing carbon atoms and formed on the underlying layer can beefficiently dry-etched without etching the underlying layer containingcarbon atoms by using a gas containing oxygen atoms and carbon atoms.Further, as shown in FIG. 3, it is clearly understood that the sameeffect can be attained even when only a CO gas is used without using anoxygen gas (that is, even when a CO gas is 100%).

[0058] Further, in the first embodiment, a case wherein a CO gas is usedas an ashing gas is explained, but in this invention, as a gascontaining carbon atoms, the following materials can be used byadequately controlling the pressure, temperature, power and the like.That is, it is possible to use CO₂, C₅H₁₂, C₅H₁₀, C₄H₁₀, C₄H₈, C₄H₆,C₃H₉N, C₃H₈, C₃H₆O, C₃H₆, C₃H₄, C₂N₂, C₂H₇N, C₂H₆O, C₂H₆, C₂H₄O, C₂H₄,C₂H₂, COS, CH₅N, CH₄S, CH₄, CHN and the like and a gas containing atleast one of oxygen atoms, nitrogen atoms and hydrogen atoms in additionto carbon atoms is used.

[0059] (Second Embodiment)

[0060] Next, a second embodiment is explained with reference to FIGS. 8Ato 8E. In the second embodiment, a case wherein a CF based layer 20 isformed as an LKD layer of an interlayer insulating layer by a CVD methodis explained. The CF based layer may be formed by using a coatingmethod.

[0061] First, an LKD layer 12 with a film thickness of 500 nm is formedby coating as an interlayer dielectric on a semiconductor substrate 11formed of silicon semiconductor, for example. Then, a metalinterconnection 10 formed of aluminum, for example, is buried in thesurface portion of the LKD layer 12. An LKD layer 20 with a filmthickness of 400 nm is formed as an interlayer dielectric on the LKDlayer 12. The LKD layer 20 is a CF based CVD insulating layer. The layerforming condition at this time is CF₄/O₂= 200/50 ccm, 1 Torr, 500 W,400° C. and the LKD layer 20 is formed by microwave discharging. Anorganic based antireflection layer 15 with a film thickness 60 nm and aphotoresist 16 with a film thickness 0.6 μm are formed by coating on theabove layer. After this, the photoresist 16 is patterned by alithography technique which is well known in the art (FIG. 8A).

[0062] Next, the antireflection layer is processed with the patternedphotoresist 16 used as a mask (FIG. 8B). Then, the LKD layer 20 isetched by an RIE method using a reactive gas of C₄F₈/CO/O₂/Ar to form acontact hole with a depth of 400 nm and a pattern size of 0.2 μm. On thebottom surface of the contact hole, the metal interconnection 10 isexposed (FIG. 8C).

[0063] Next, portions of the photoresist 16 and antireflection layer 15which are left behind on the LKD layer 20 are stripped by a plasmaprocess using O₂/CO in the same ashing condition as in the firstembodiment (FIG. 8D).

[0064] After this, a TiN barrier metal layer 18 is formed to a filmthickness of approximately 30 nm and an aluminum (Al) layer 19 is formedto a film thickness of approximately 700 nm by the sputtering method andfilled in the contact hole.

[0065] After this, the Al layer 19 is polished by a CMP method until thesurface of the LKD layer is exposed. Thus, a contact interconnection ofthe aluminum layer 19 is formed in the contact hole. The contactinterconnection is used for electrically connecting an upper layerinterconnection (not shown) to the metal interconnection (lower layerinterconnection) 10 (FIG. 8E).

[0066] Stripping of the photoresist after processing the LKD layer 20 ofa CF based layer is effected by a plasma ashing process using an oxygengas in the conventional method, but according to this method, thereoccurs a problem that the side surface of the LKD layer 20 of a CF basedlayer is side-etched at the same time as the upper portion thereof isetched and a CD bias occurs. This is because ion assisted etching of thephotoresist due to an oxygen ion and oxygen radical occurs in the lowpressure oxygen RIE process, an isotropic oxygen radical componententers the contact hole and a process for etching the interlayerdielectric 20 of a CF based layer proceeds from a portion which is incontact with the radical based gas. Further, since ions are dispersed invarious directions other than the vertical direction, ion assistedetching occurs in the side wall.

[0067] As described above, in the second embodiment, the organic basedantireflection layer and the layer (photoresist) containing carbon atomsand formed on the underlying layer can be efficiently ashed withoutetching the insulating layer containing carbon atoms and used as theunderlying layer by using a gas containing carbon atoms or a gascontaining oxygen atoms and carbon atoms. As shown in FIG. 3, the sameeffect can be attained even when only a CO gas is used without using anoxygen gas. In the second embodiment, a CF based layer is used as theinsulating layers, but another organic layer can be used.

[0068] Further, in the second embodiment, a Co gas is used as ashinggas, but as a gas containing carbon atoms, the following materials canbe used by adequately controlling the pressure, temperature, power andthe like. That is, it is possible to use CO₂, C₅H₁₂, C₅H₁₀, C₄H₁₀, C₄H₈,C₄H₆, C₃H₉N, C₃H₈, C₃H₆O, C₃H₆, C₃H₄, C₂N₂, C₂H₇N, C₂H₆O, C₂H₆, C₂H₄O,C₂H₄, C₂H₂, COS, CH₅N, CH₄S, CH₄, CHN and the like and a gas containingat least one of oxygen atoms, nitrogen atoms and hydrogen atoms inaddition to carbon atoms is used.

[0069] The metal interconnection is not limited to aluminum. Forexample, Al—Si—Cu, Al—Cu, W, WSi, Cu, Ag, Au or the like can be used.Further, this invention is not limited to the contact hole shown in thesecond embodiment and the same effect can be attained wheninterconnection grooves or other patterns are formed.

[0070] (Third Embodiment)

[0071] Next, a third embodiment is explained with reference to FIGS. 9Ato 9K. In the third embodiment, a porous and relatively fragileinorganic based layer is used as an LKD layer of an interlayerdielectric. That is, an interconnection structure having a structure inwhich a carbon based layer is buried in the porous insulating layerwhich is used for forming a gas dielectric structure in the underlyinglayer is explained.

[0072] A porous silicon oxide layer 22 is formed on a silicon nitridelayer 21 with a film thickness 500 nm which is formed on a semiconductorsubstrate 11 by a CVD method. An organic based antireflection layer 15with a film thickness 60 nm and a photoresist 16 with a film thickness0.6 μm are formed by coating on the above-mentioned layer. After this,the photoresist 16 is patterned by a lithography technique which is wellknown in the art (FIG. 9A).

[0073] Next, the antireflection layer 15 is processed with the patternedphotoresist used as a mask (FIG. 9B). Then, the porous silicon oxidelayer 22 is etched by an RIE method using a gas of C₄F₈/CO/O₂/Ar withthe silicon nitride layer 21 used as an etching stopper to forminterconnection grooves with a depth of 400 nm and a pattern size of 0.3μm square at an interval of 0.3 μm (FIG. 9C).

[0074] Next, portions of the photoresist 16 and antireflection layer 15which are left behind on the porous silicon oxide layer 22 are strippedby oxygen downflow ashing (FIG. 9D). After this, a carbon layer 23 isformed to a film thickness of 700 nm by sputtering and filled in thegrooves formed in the porous silicon oxide layer 22. The carbon layer isan extremely rigid or strong layer in comparison with the photoresistand antireflection layer and the carbon concentration thereof is two tothree times that of the latter layers.

[0075] In this embodiment, the CVD method is used to form the poroussilicon oxide layer 22, but a coating method can also be used insteadthereof. After this, the carbon layer 23 is polished by a CMP methoduntil the surface of the porous silicon oxide layer 22 is exposed (FIG.9E).

[0076] An antireflection layer 25 with a film thickness of 60 nm and aphotoresist 26 with a film thickness of 0.6 μm are formed by coating onthe porous silicon oxide layer 22 and carbon layer 23. After this, thephotoresist 26 is patterned by a lithography technique which is wellknown in the art (FIG. 9F).

[0077] After the antireflection layer is processed with the photoresist26 used as a mask, the underlying carbon layer 23 is etched by an RIEmethod using a gas of C₄F₈/CO/O₂/Ar to form interconnection grooves 24with a depth of 200 nm and a pattern size of 0.2 μm (FIG. 9G). Further,portions of the photoresist 26 and antireflection layer 25 which areleft behind on the porous silicon oxide layer 22 are stripped by anashing process (FIG. 9H).

[0078] After this, a TiN barrier metal layer 18 is formed to a filmthickness of approximately 30 nm on the inner wall of interconnectiongrooves 23′ and then an aluminum (Al) layer 19 is formed to a filmthickness of 700 nm by sputtering and filled in the interconnectiongrooves 23′. Then, the Al layer 19 is polished by a CMP method until thesurface of the porous silicon oxide layer 22 is exposed. As a result,the Al layer 19 used as contact interconnections is formed and buried inthe carbon layer 23 (FIG. 9I).

[0079] After this, a porous silicon oxide layer 22′ with a filmthickness of 100 nm is formed by a CVD method, for example, to cover theAl layers 19 buried in the respective carbon layers 23 (FIG. 9J). Then,the carbon layer 23 in the porous silicon oxide layer 22 which is anunderlying layer of the porous silicon oxide layer 22′ is etched byoxygen downflow ashing. As a result, midair interconnections formed ofthe Al layers 19 covered with the porous silicon oxide layer 22′ andarranged in the grooves of the porous silicon oxide layer 22 in whichthe carbon layers 23 have been buried are formed. If the carbon layer 23is ashed, carbon becomes carbon dioxide gas and is dispersed through theporous portions of the porous silicon oxide layers 22 and 22′ to theexterior to make hollows around the TiN barrier metal layers 18 and Allayers 19. In the semiconductor device explained in the thirdembodiment, a plurality of interconnection grooves as described aboveare formed and the dielectric constant of the interlayer dielectric isfurther lowered (FIG. 9K).

[0080] In a process for stripping portions of the photoresist 26 andantireflection layer 25 which are left behind on the porous siliconoxide layer 22 by the plasma process after the interconnection grooves23′ are formed in the carbon layers 23, there occurs a problem in theconventional method that the carbon layer 23 formed in the poroussilicon oxide layer 22 which is the underlying layer is etched. This isbecause the porous silicon oxide layer 22 may permit the oxidationradical to freely pass therethrough and, as a result, there occurs aproblem that the CD bias occurs.

[0081] Therefore, the third embodiment has a feature that the processfor stripping portions of the photoresist 26 and antireflection layer 25which are left behind on the porous silicon oxide layer 22 by the plasmaprocess after formation of the interconnection grooves is effected by aplasma process using a gas containing carbon atoms or a gas containingoxygen atoms and carbon atoms. The ashing device is of a parallel platetype shown in FIG. 2 and the ashing condition is O₂/CO=100/200 ccm, 100m Torr, 500 W and 30° C. In this condition, the process for strippingthe photoresist 26 proceeds, and since etching of the carbon layer 23can be suppressed, occurrence of the CD bias can be prevented.

[0082] Thus, the effect of suppressing the side etching of groovesformed in the underlying layer containing carbon atoms is particularlyhigh in a region in which the percentage of carbon atoms is higher than⅓of the percentage of oxygen atoms in a gas containing carbon atoms or aprocess gas containing oxygen atoms and carbon atoms. Further, the sideetching can be suppressed while a sufficiently high etching rate is keptby effecting the process at 150° C. or less by the RIE method. The sideetching can be more effectively suppressed by effecting the process at400 m Torr or less.

[0083] The metal interconnection is not limited to aluminum. Forexample, Al—Si—Cu, Al—Cu, W, WSi, Cu, Ag, Au or the like can be used.

[0084] Further, in the above embodiment, a CO gas is used as the ashinggas, but as a gas containing carbon atoms, the following materials canbe used by adequately controlling the pressure, temperature, power andthe like. That is, it is possible to use CO₂, C₅H₁₂, C₅H₁₀, C₄H₁₀, C₄H₈,C₄H₆, C₃H₉N, C₃H₈, C₃H₆O, C₃H₆, C₃H₄, C₂N₂, C₂H₇N, C₂H₆O, C₂H₆, C₂H₄O,C₂H₄, C₂H₂, COS, CH₅N, CH₄S, CH₄, CHN and the like and a gas containingat least one of oxygen atoms, nitrogen atoms and hydrogen atoms inaddition to carbon atoms is used. In this embodiment, a case of theinterconnection grooves is explained, but the same effect can beattained when contact holes or other patterns are formed.

[0085] Further, the parallel plate ashing device is used for the plasmaprocess, but another type of plasma ashing device can be used. Further,for example, a downflow asher device can be used by adequatelycontrolling the pressure, temperature and power.

[0086] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A dry etching method comprising the steps of:sequentially laminating a first insulating layer containing carbon and asecond insulating layer containing carbon on a substrate; patterning thesecond insulating layer into a preset shape; forming grooves in thefirst insulating layer by etching the first insulating layer with thesecond insulating layer used as a mask; and removing the secondinsulating layer by use of a reactive gas containing carbon atoms and atleast one of oxygen atoms, hydrogen atoms and nitrogen atoms withoutsubstantially modifying or deforming the side surface of the grooves inthe first insulating layer.
 2. The dry etching method according to claim1 , wherein the first insulating layer containing carbon atoms is oneselected from a group consisting of a carbon layer, an organic siliconcompound layer and an organic layer.
 3. The dry etching method accordingto claim 1 , wherein the second insulating layer containing carbon is aphotoresist.
 4. The dry etching method according to claim 1 , whereinthe second insulating layer containing carbon is an organicantireflection layer.
 5. The dry etching method according to claim 1 ,wherein an atomic percentage of carbon is not less than ⅓of that ofoxygen in a gas containing carbon atoms and oxygen atoms among the gascontaining carbon atoms and at least one of oxygen atoms, hydrogen atomsand nitrogen atoms.
 6. The dry etching method according to claim 5 ,wherein a gas selected from the group consisting of a gas containingoxygen and carbon dioxide, a gas containing oxygen and carbon monoxide,a carbon monoxide gas and a carbon dioxide gas is used as the gascontaining oxygen atoms and carbon atoms.
 7. The dry etching methodaccording to claim 1 , wherein said step of removing the secondinsulating layer includes a step of setting the substrate temperature tonot higher than 150° C.
 8. The dry etching method according to claim 1 ,wherein said step of removing the second insulating layer includes astep of setting the reaction pressure to not higher than 400 m Torr. 9.A semiconductor device manufacturing method comprising the steps of:sequentially laminating an insulating layer and a photoresist eachcontaining carbon on a semiconductor substrate; patterning thephotoresist into a preset shape; forming at least one of contact holesand interconnection grooves in the insulating layer by etching theinsulating layer with the photoresist used as a mask; ashing andremoving the photoresist by use of a gas containing carbon atoms and atleast one of oxygen atoms, hydrogen atoms and nitrogen atoms; anddepositing a metal interconnection layer in at least one of the contactholes and the interconnection grooves to form interconnections therein.10. The semiconductor device manufacturing method according to claim 9 ,wherein the insulating layer containing carbon is one of an organicsilicon compound layer and an insulating layer of low dielectricconstant containing carbon atoms.
 11. The semiconductor devicemanufacturing method according to claim 9 , wherein an atomic percentageof carbon is not less than ⅓of that of oxygen in a gas containing carbonatoms and oxygen atoms among the gas containing carbon atoms and atleast one of oxygen atoms, hydrogen atoms and nitrogen atoms.
 12. Thesemiconductor device manufacturing method according to claim 9 , whereina gas selected from the group consisting of a gas containing oxygen andcarbon dioxide, a gas containing oxygen and carbon monoxide, a carbonmonoxide gas and a carbon dioxide gas is used as the gas containingoxygen atoms and carbon atoms.
 13. The semiconductor devicemanufacturing method according to claim 9 , wherein said step ofremoving the second insulating layer includes a step of setting thesubstrate temperature to not higher than 150° C.
 14. The semiconductordevice manufacturing method according to claim 9 , wherein said step ofremoving the second insulating layer includes a step of setting thereaction pressure to not higher than 400 m Torr.
 15. A semiconductordevice manufacturing method comprising the steps of: sequentiallylaminating an insulating layer and a first photoresist on asemiconductor substrate; patterning the first photoresist into a presetshape; forming first interconnection grooves by etching the insulatinglayer with the first photoresist used as a mask; ashing and removing thefirst photoresist by use of a gas containing carbon atoms and at leastone of oxygen atoms, hydrogen atoms and nitrogen atoms; burying a carbonlayer in the first interconnection grooves; laminating a secondphotoresist on the insulating layer to cover the carbon layer;patterning the second photoresist into a preset shape; forming secondinterconnection grooves by etching the carbon layer with the secondphotoresist used as a mask; ashing and removing the second photoresistby use of a gas containing carbon atoms and at least one of oxygenatoms, hydrogen atoms and nitrogen atoms; depositing a metalinterconnection layer in the second interconnection grooves to buryinterconnections therein; forming a porous silicon oxide layer on theinterlayer insulating layer to cover the interconnections and the carbonlayer; and heating the carbon layer to remove the same from theinterconnection grooves and provide a hollow around each of theinterconnections.
 16. The semiconductor device manufacturing methodaccording to claim 15 , wherein at least one of said step ofsequentially laminating an insulating layer and a first photoresist on asemiconductor substrate and said step of laminating a second photoresiston the insulating layer to cover the carbon layer further includes astep of forming an antireflection layer between the insulating layer anda corresponding one of the first and the second photoresist.
 17. Thesemiconductor device manufacturing method according to claim 15 ,wherein an atomic percentage of carbon is not less than ⅓of that ofoxygen in a gas containing oxygen atoms and carbon atoms among the gascontaining carbon atoms and at least one of oxygen atoms, hydrogen atomsand nitrogen atoms.
 18. The semiconductor device manufacturing methodaccording to claim 15 , wherein a gas selected from the group consistingof a gas containing oxygen and carbon dioxide, a gas containing oxygenand carbon monoxide, a carbon monoxide gas and a carbon dioxide gas isused as the gas containing oxygen atoms and carbon atoms.
 19. Thesemiconductor device manufacturing method according to claim 15 ,wherein said step of ashing and removing the photoresist includes a stepof setting the substrate temperature to not higher than 150° C.
 20. Thesemiconductor device manufacturing method according to claim 15 ,wherein said step of ashing and removing the photoresist includes a stepof setting the reaction pressure to not higher than 400 m Torr.